SPDSS_Task1_Research-ID-StudyPeriod

• Title: SPDSS Task 1 - Research and Identify Appropriate Study Period
• Description: The objective of this task was to verify or refine the recommended study period as follows: 1. Review the availability and reliability of digitized data required for the development of DSS components; 2. Determine that the period includes wet, dry, and average periods; represents the long-term average hydrology of the basin; and allows for cost-effective modeling efforts; 3. Document study periods used in other modeling efforts in the South Platte Basin.
• Decision Support - Doc Type: Task Memorandum
• Date: 10/26/2003
• DSS Category: Surface Water
• DSS: South Platte
• Basin: South Platte
• Contract/PO #: C153954
• Grant Type: Non-Reimbursable
• Bill Number: SB01-157, HB02-1152, SB03-110, HB04-1221, SB05-084, HB06-1313, SB07-122
• Prepared By: Leonard Rice Engineering

shown, and summarized in Table 2, the long term average hydrology represented by the
average streamflow for the total period of record is reflected in the 1950 to 2002 average
streamflow to within 7 percent for gages unaffected by major upstream transbasin
diversions -the first four gages listed in Table 2.
Figure 2
Example of Annual streamflow
Middle Boulder Creek at Nederland, CO (06725500)
70,000
60,000
50,000
40,000
m
3
i° 30,000
20,000
10,000
Year
The following comments address gages shown in Table 2 where the average annual flow
for the 1950 through 2002 period varies more than 3 percent from the total period of
record flow:
At the Cherry Creek near Franktown station, the low flow conditions often result in
numerous estimated records, which could explain a larger percent difference between
average streamflows for the two periods.
At the Big Thompson River at the Mouth of the Canyon near Drake, the commission
of Olympus Tunnel in May 1955 resulted in diversion of natural streamflow from the
Big Thompson River. Therefore, the average annual flow for the 1950 through 2002
period is 15 percent less than the average annual flow for the total period of record.
The Cache La Poudre River at Mouth at Mouth of Canyon Near Fort Collins gage
reflects diversions through the Monroe Tunnel (average of 32,000 acre-feet per year),
built in the early 1950s as part of the North Poudre Canal system. These diversions
are exchanged for CBT water that is delivered downstream of the gage. Therefore,
the average flow for the 1950 through 2002 period is 12 percent less than the average
annual flow for the total period of record.
The South Platte River at Julesburg gage clearly shows the increases in transbasin
diversions and storage in the basin during the proposed study period.
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